As known in the art, generators are provided with a stator and a rotor connected to a motor (such as a steam or a gas turbine) for rotating it within the stator and generating electric power.
The stator is provided with an electric winding (that collects the electric power) that is connected to lead conductors coupled to bushings.
The bushings are typically connected to an electric user or a transformer or an electric line.
In large power electric generators (for example 500 MW or more) during operation a large amount of heat is generated at the connection between the lead conductors and the bushings; such heat must be removed (i.e. the lead conductors and the bushings must be cooled) in order to safeguard the reliability of the generator.
In this respect, lead conductors and bushings are misaligned from one another and are connected each other via metallic clamps.
In addition, the lead conductors and the bushings are tubular in shape and are connected to Teflon pipes carrying a cooling fluid, such that during operation the cooling fluid passes through the Teflon pipes and the lead conductors to cool the lead conductors (it is then fed to the generator stator), and further fluid passes through further Teflon pipes and the bushings to cool the bushing.
Nevertheless this arrangement has some drawbacks.
First of all assembling is very complicated and time consuming, due to the large number of Teflon pipes to be connected (the zone of the generator where the Teflon pipes must be connected is often very small, this increases the difficulty of assembling).
In addition, the Teflon pipes are directly connected to the lead conductors and the bushings, i.e. they are connected to parts of the generator having high tension; this causes the need of a minimum length of the Teflon pipes in order to guarantee a sufficient dielectric strength to avoid electrical discharges.
GB 725,211 discloses a sealed electrical generator having a high pressure chamber housing the stator and the rotor, and a low pressure chamber housing the electrical connection between the lead conductors (connected to the winding of the generator stator) and the bushings.
This generator is provided with a cooling system for the bushings.
The cooling system comprises a duct within each bushing and an injector having an end opened in the high pressure chamber and the other end opened in the low pressure chamber and aligned with the duct of the bushing, but away from it.
During operation the cooling fluid (being the gas filling the sealed generator) enters the injectors in the high pressure chamber and is injected into the ducts of the bushings in the low pressure chamber (thanks to the differential pressure); then the cooling fluid passes through the bushings and cools them.
Nevertheless also this arrangement has some drawbacks.
In fact, cooling is not efficient, since the cooling fluid is injected from an injector and must enter a duct that is away from the same injector.